Added modal double faces cards implementation (MDF cards, #7012)

Mage/src/main/java/mage/cards/ModalDoubleFacesCardHalf.java

@@ -0,0 +1,18 @@
+package mage.cards;
+
+import mage.MageInt;
+
+/**
+ * @author JayDi85
+ */
+public interface ModalDoubleFacesCardHalf extends Card {
+
+    @Override
+    ModalDoubleFacesCardHalf copy();
+
+    void setParentCard(ModalDoubleFacesCard card);
+
+    ModalDoubleFacesCard getParentCard();
+
+    void setPT(MageInt power, MageInt toughtness);
+}